The A1C test is a blood test that measures a person’s average blood glucose levels over the past 3 months. Blood glucose is another name for blood sugar.
Doctors use the A1C test to check for:
- type 1 diabetes
- type 2 diabetes
This test also helps doctors monitor blood glucose levels in people with diagnosed diabetes.
Keeping A1C levels within the normal or target range lowers the risk of developing diabetes or its complications. Read on to learn what A1C test results mean.
The A1C chart below can help a person convert and understand their A1C test results. The doctor can provide more context and describe ways to keep blood glucose levels in a safe range.
The A1C test is also known as the:
- hemoglobin A1C, or HbA1c, test
- glycated hemoglobin test
- glycohemoglobin test
The A1C test measures the percentage of red blood cells that have glucose-coated hemoglobin. This measurement gives doctors an idea of the person’s average blood glucose levels over the past 2–3 months.
Hemoglobin is an iron-rich protein in red blood cells. It helps carry oxygen from the lungs to other tissues.
When glucose enters the blood, it binds to hemoglobin. The more glucose in a person’s bloodstream, the more hemoglobin is bound to glucose.
Undergoing the A1C test is straightforward: A healthcare professional takes a blood sample and sends it to a laboratory for testing.
A doctor may order this test to:
- diagnose prediabetes
- diagnose type 1 or type 2 diabetes
- monitor the blood glucose levels of a person with diabetes to check how well their treatment is working
If a person takes insulin to manage diabetes, their doctor may also ask them to monitor their blood glucose levels at home with a blood glucose meter or continuous glucose monitor.
In this case, the person still needs to undergo regular A1C testing.
Traditionally, A1C levels are reported as a percentage. Alternately, they may be reported as estimated average glucose (eAG), in milligrams per deciliter (mg/dL) or millimoles per liter (mmol/L).
Blood glucose meters and continuous glucose monitors also give eAG readings, some from at least 12 days of data.
The A1C test gives a more accurate long-term average. It takes into account fluctuations throughout the day, such as overnight and after meals.
A normal A1C level is below 5.7%. Normal eAG is below 117 mg/dL or 6.5 mmol/L.
If someone’s A1C levels are higher than normal, they may have diabetes or prediabetes. Their doctor might order a repeat test to confirm this.
Target levels in people with diabetes
A doctor will set a person’s target A1C level based on many factors. The right target varies from person to person.
For someone with diabetes, the target A1C level may depend on:
- the person’s age
- their overall health
- whether they are pregnant
- how long they have had diabetes
- their prescribed treatment plan
- any history of adverse effects from the treatment, including episodes of low blood glucose, or hypoglycemia
- any complications from diabetes
- the person’s preferences and treatment priorities
In general, a doctor might recommend aiming for A1C levels under 6.5% if a person:
- is young and has a long life expectancy
- has had diabetes for a short period
- is effectively managing their diabetes with lifestyle changes or metformin alone
- is otherwise in good health
A doctor might recommend A1C targets of 7.0–8.5% if a person:
- is older and has a shorter life expectancy
- has had diabetes for a longer period
- has diabetes that is hard to manage, even with multiple medications
- has a history of severe hypoglycemia or other adverse effects of treatment
- has experienced complications of diabetes
- has other chronic health conditions
A person should work with their doctor to reassess and adjust their A1C targets over time. The condition and treatment goals may change.
To screen for diabetes, a doctor may order an A1C test for someone older than 45. They may also do this for younger people who have other risk factors.
After diagnosing diabetes, a doctor determines how often to test A1C levels.
If a person is meeting their treatment goals, they may need an A1C test twice a year. When managing blood glucose levels is challenging, a person tends to need this test more frequently.
A person should make an appointment with their doctor if they:
- have questions or concerns about their treatment plan
- are finding it hard to keep their blood glucose levels within the target range
- have had symptoms of high or low blood glucose levels
- think they might have complications of diabetes
Symptoms of high blood glucose levels include:
- unusual thirst
- frequent urination
- blurred vision
Symptoms of low blood glucose levels include:
- nervousness, irritability, or anxiety
Anyone who develops any of the symptoms above or notices other changes in their health should let their doctor know.
A doctor orders an A1C test to check whether someone has prediabetes or type 1 or 2 diabetes. Doctors also use this test to monitor blood glucose levels in people with diabetes to see how well their treatment plan is working.
A1C test results are usually a percentage, but they may come as an eAG measurement. Target A1C levels vary from person to person, depending on age, overall health, and other factors.
Having high A1C levels may indicate that the person has diabetes or a high risk of related complications. In this case, the doctor will work with the person to adjust the approach to treatment.